Missouri

Missouri (abbrev: MO) became the 24th state of the United States of America on August 10, 1821, a mere 18 years after having been thrown in as a lagniappe with the Louisiana Purchase. President Thomas Jefferson purchased the Louisiana territory from France in 1803, a win-win situation for the United States, France, and Spain. The United States doubled its size, France got rid of an annoying distraction in the New World so Napoleon could focus on conquering Europe, and Spain could stop pretending it owned the place. As a result, Missouri is absolutely nuts over Thomas Jefferson and France, going so far as to name its capital after Jefferson and its 2nd biggest city after St. Louis, the only canonized king of France. There's even a statue of Thomas Jefferson at the capitol building.

Missouri is about as close to the center of the United States as one can get without actually being Kansas (a distinction no state really wants). Its borders are like so:

The Mississippi River marks the border between Illinois and Missouri, as it does between all proper states up until Minnesota, which has so many lakes it never even noticed that the Mississippi was inside of it until someone pointed it out to them. Rather than admit their mistake, they found the source of the river and declared a state park around it.

Being the most central, Easternmost point in the Louisiana Purchase, Missouri became known as the "Gateway to the West", basically an admission that the state is really just an area to pass through on your way to more interesting places. Oddly enough, it's also known as the bizarrely hyphenated "Show-Me State", although what there is to see in Missouri is still unknown†. To commemorate the millions of people who have passed through St. Louis without stopping longer than necessary to gather fresh supplies, they built the Gateway Arch in 1965. For its location, they chose the starting point of the Lewis and Clark expedition, historically the first people to leave Missouri as quickly as possible to go find something more interesting. Later, in 2003, Missouri honored Lewis and Clark's triumphant return in the design for their state quarter, as this is the only recorded instance of someone actually coming back to Missouri after having left.

† LaggedyAnne informs me that the phrase refers to the stubborn nature of Missouri natives, who refuse to simply take another person's word and must be shown before they will accept it. Thanks!

Of course, you can't really get a feel for what a state is like without comparing it to one of the others. It's statistically provable that Ohio is the baseline example for a minimally livable state (although the proof of this is outside of the scope of this article). One is tempted to compare Missouri to Illinois, but it wouldn't be fair to expect St. Louis to compete with Chicago.